LOUD cold start knock ... goes away in 20-30 seconds after startup

I recently noticed a LOUD cold start knock that my truck appears to have developed. It only happens after the truck's sat overnight or without being run for a while. It's loud enough to have given me pause ... but it's gone in 20-30 seconds as oil gets to moving around and the vehicle commences its warm-up.

Doing some reading, online, it appears that this is 'normal' for 5.3L Vortecs ... and that it isn't harmful. I'd like some confirmation of that from sources I trust, hence this post.

I've also read that Seafoam may help. Now, I've never been a believer that dumping some brand of snake oil into the tank can help, but I've read enough about Seafoam to know some, here, have used it and claimed positive results. Do folks, here, think it'll make a difference? If so, what's the best way to use it for this issue?

I've read about people dumping it in the tank, about them using a vacuum line to get it into the engine, about putting it in the oil ... I'm just not sure what the best way to 'feed' it to the engine might be for this issue -- if it's even worth doing.

Opinions from those with this issue and/or Seafoam wanted. (Others considered, as well!)

-- Surreal

P.S. [MENTION=54249]RayVoy[/MENTION] and [MENTION=51590]Pikey[/MENTION] I'm particularly interested in your input as to what I should do and how I should go about it.

Yea its common, its gets worse with carbon so seafoam is good way to get rid of it. Mine only does it around freezing and below and it an 01 with no issues. Look up piston slap to study it more its mostly from the short piston skirts that allow the piston to rock around more when cold. Also different oils help, i run moble 1 truck 5w30 in my truck with 116k on it. I have heard that gm top end cleaner and the 3m kits work well. I would reccomend getting an IV type setup so it distributes more evenly in the engine and wont flood it.

Unlike snake oil products SeaFoam is EPA certified for use in engines to clean them. Running SeaFoam through the oil 50-110 miles before and oil change cleans out the oil and really helps to stop the tick/knock. My 96 had this last month and the tick would last about a min and then stop. All vehicles with Hydraulic lifters can have this happen. Mine was caused more from being about a quart low on oil (losing it from a small leak). Also some like [MENTION=51590]Pikey[/MENTION] say after market oil filters can contribute to this ticking as the oil gets older.

More on the SeaFoam now. If you go to their site they explain everything about how to use the product and even have videos of it being used on a mid 2000's Silverado with a Vortec. In my case I only put it in the oil and tank because I didn't want to play with my vacuum lines. So far they truck has run fairly good with it and I changed the oil after 50+ miles of the SeaFoam doing its work. The start up tick is now totally gone and the engine oil seems to stay at a steadier pressure. BTW SeaForm says that if your not satisfied my their product they will refund your money no questions asked.

My 2002 did the same thing below freezing. I drove it for another 30,000 miles, before selling it, with no issues. I still speak with the guy that bought it. He has 180,000 (80,000 miles from when the slap started) miles on it and still no issue. I ran mobile 1 and royal purple from the day I purchased the truck (new from the dealer) the sound never changed with a fresh oil change.

I am not a believer in adding anything to my crankcase oil. When I worked in the garage it seemed like every time we added an "engine cleaner" to the oil the motor blew. A few months ago my nephew went to a quick oil change place and they talked him into a "engine cleaning". They added it to his oil, ran it for 15 minutes, drained the oil, changed the filter and refilled with oil. On his way home, the truck with 101,000 miles on it threw a rod, popped it right out of the side of the block. I know people that add marvel mystery oil and sea foam to their crankcase with no issues. They put it in drive for a few hundred miles and change the oil and filter. I will not do it. It may work, it may not. I feel like adding a thin solvent like substance (I don't think that sea foam is considered a solvent) cuts the viscosity of the oil.

I have sucked the seafoam in thru the brake booster vacuum line. This made me nervous due to the chance of hydro lock if you suck too much in too fast. It stopped much of the valve train noise and smoothed out the idle on my 2003 for a few months. I sucked it in, let it sit for 20 minutes, then started it up and watched the smoke show. If you have a hydro boost rather than vacuum booster, i have seen seafoam in an aerosol can that says you can just spray it into your throttle body. I do run sea foam thru my gas tank once every oil change.

Really, as with modding, it is your truck. Do what you wish with it. If it really bothers you, then try something. If you can live with it, then do just that. It would bother me enough that I might try adding a bottle to the fuel tank and sucking in half a can into the intake. If that did not change anything at all, I might just live with the noise. Again, I am not a fan of adding things to my oil. Of course this is just my opinion.

Unlike snake oil products SeaFoam is EPA certified for use in engines to clean them.

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EPA certified just has to do with the Environmental protection agency. It basically means that the product will not harm the environment too badly when used. It has nothing to do with it's cleaning abilities.

EPA certified just has to do with the Environmental protection agency. It basically means that the product will not harm the environment too badly when used. It has nothing to do with it's cleaning abilities.

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I understand that I was more pointing out that unlike most products from other manufactures that aren't even tested at all by federal agencies. Personally I don't care much about that I was more listing off facts.

I recently noticed a LOUD cold start knock that my truck appears to have developed. It only happens after the truck's sat overnight or without being run for a while. It's loud enough to have given me pause ... but it's gone in 20-30 seconds as oil gets to moving around and the vehicle commences its warm-up.

Doing some reading, online, it appears that this is 'normal' for 5.3L Vortecs ... and that it isn't harmful. I'd like some confirmation of that from sources I trust, hence this post.

I've also read that Seafoam may help. Now, I've never been a believer that dumping some brand of snake oil into the tank can help, but I've read enough about Seafoam to know some, here, have used it and claimed positive results. Do folks, here, think it'll make a difference? If so, what's the best way to use it for this issue?

I've read about people dumping it in the tank, about them using a vacuum line to get it into the engine, about putting it in the oil ... I'm just not sure what the best way to 'feed' it to the engine might be for this issue -- if it's even worth doing.

Opinions from those with this issue and/or Seafoam wanted. (Others considered, as well!)

-- Surreal

P.S. @RayVoy and @Pikey I'm particularly interested in your input as to what I should do and how I should go about it.

Click to expand...

I seem to remember you mentioning that my 5.3L sounds like a diesel when we started it up cold, and the noise went away once the engine warmed up....

I want to officially welcome you to the "High Mileage 5.3L owners club". The lifters are cheap and horrid and have an issue sticking, and unfortunately, at some point oil issues will start showing up.

In your case, you may just pull the engine and rebuild it with the "right" parts and not the parts GM put in it from the factory.

The morning sickness knock can come from two areas (assuming engine wear is normal for the mileage), the lifters and piston slap (as has been suggested).

Neither one will hurt the engine, just piss off the owner.

It is my experience, the piston slap goes away inside the first minute, the lifter noise will last longer and may still be there when the engine is warm.

I don't think there is anything (maybe a rebuild) that will fix the piston slap. The lifter noise is usually dirt and, or wear, that lets the lifter "bleed down". Sometimes as @Conlan Rose suggested, it might be a slow to build oil pressure issue, that is caused by a dirty oil filter, sometimes it's clogged oil passages.

Like you [MENTION=50075]SurrealOne[/MENTION] and @Pikey and some of the others, I'm not a big fan of additives. An old mechanic, that I knew as a kid, wanted me to add kerosene to the oil to clean out the noisy lifters. I decided to change the lifters, haha.

And, because of my reluctance to add cleaners to my truck, I can not recommend adding them to yours. But, I will discuss as long as you wish.

very surprised no one mentioned marvel mystery oil. any carbon or lifter issues this product when properly used does clean and lube these components to reduce engine noise. this is not a solvent like seafoam or kerosene etc.. this does a very good job reducing this noise issue. I have a 2000 5.3L and I have used this product for 13 years now . my 140,ooo mi. engine is quieter now than new. must have been a dirty new engine because after using this product with the pure one purloator and wix oil filters the engine runs perfect[synthetic oil]. I don't have any issues at all with it . just did a 1000mi trip got 18.5 MPG no oil usage .

piston knock on starting and not in gear is not a normal or good condition. lifter noise is just some carbon in the lifter or you have antifreeze in the crankcase.

using seafoam by vacuum injection has destroyed some engines if not properly done. so much can get into a cylinder it will damage the rings/cylinder wall. adding to the engine oil before an oil change will quickly remove the sludge and some carbon.

I have used seafoam, gm top end cleaner and the 3m kit and they seem to work so I didnt bother with anything else. As an additive i do like the justice brothers stuff and haveused it in borh customers and my own engines. Like i said before i would HIGHLY reccomend the can IV vacuum line thing because i too get paranoid about hydrolocking. I do suspect i have one or 2 noisy lifters but other than some noise i have had no issues. When she starts getting higher miles i think i will rebuild it with a bigger cam and light stuff but for now i gut let it idle for a min before dropping it in gear.